Women with gestational diabetes reduced their risk of progressing to type 2 diabetes by more than half if they exclusively breastfed their infants, compared with women who fed their babies exclusively with formula, according to a new study.
Researchers also found that breastfeeding for more than 2 months was associated with a lower incidence of progression to type 2 diabetes.
“In our study, both higher lactation intensity and duration showed strong, graded protective associations with type 2 diabetes mellitus incidence, independent of risk factors (sociodemographic characteristics, prenatal metabolic status and course, perinatal outcomes, and lifestyle behaviors) that were not explained by weight loss,” Erica P. Gunderson, Ph.D., of Kaiser Permanente Northern California, and her associates wrote.
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The researchers initially evaluated 1,035 women who had been diagnosed with gestational diabetes mellitus (GDM) and had a singleton delivery at 35 weeks’ gestation or later, but followed only the 1,010 women without type 2 diabetes at 6-9 weeks postpartum. Of the 959 women evaluated at the end of the 2-year follow-up, 11.8% had progressed to type 2 diabetes (Ann Intern Med. 2015 Nov 24. doi:10.7326/M15-0807).
Data on breastfeeding intensity and duration were collected through feeding diaries, phone calls, in-person exams, and monthly mailed questionnaires. The four categories of intensity included exclusive lactation, mostly lactation (about 1-6 ounces of formula per 24 hours), mostly formula (more than 17 ounces per 24 hours), and mixed feeding (7-17 ounces of formula per 24 hours). These categories were compared to exclusive formula feeding.
Compared with mothers who exclusively fed their infants formula, mothers who exclusively breastfed had a 54% lower risk of developing type 2 diabetes (hazard ratio, 0.46). The risk of developing type 2 diabetes was 46% lower for women who mostly breastfed, and women who mostly used formula or who mixed formula and breastfeeding had a 36% reduced risk (HR, 0.54 and 0.64, respectively; P trend = 0.016).
Similarly, duration of breastfeeding correlated with the reduced risk of developing diabetes. Compared with mothers who breastfed their infants from 0 to 2 months, those who breastfed for longer than 10 months had a 57% lower risk of developing type 2 diabetes. Women who breastfed their infants for 5-10 months had a 50% lower risk, and those who breastfed from 2 to 5 months had a 45% lower risk, compared with those breastfeeding up to 2 months.
“Potential mechanisms to explain the lower incidence of [diabetes mellitus] with higher intensity and duration of lactation include preservation of pancreatic beta cells, less inflammation, and improved endothelial function; however, biochemical evidence is sparse,” the researchers wrote, noting the effect prolactin has during pregnancy on increasing pancreatic beta-cell mass and function.
In analyzing the relationship between development of type 2 diabetes and lactation duration and intensity, the researchers controlled for a range of confounders. These included maternal body mass index, gestational diabetes treatment, prepregnancy weight, maternal delivery weight, delivery method, and newborn outcomes (birth weight, length, gestational age, Apgar score, hospital stay duration, medical diagnoses, and NICU admission). Researchers also accounted for lifestyle behaviors, depression, medication use, maternal education, parity, age, race/ethnicity, and health history.
The research was funded by the National Institutes of Health, Kaiser Permanente Northern California, and the W.K. Kellogg Foundation. Dr. Gunderson has received grant funding from the American Diabetes Association. Other authors reported receiving industry grants outside of this study.